In recent years, image editing apparatus have been required to realize a variety of advanced image effects in simple processing. For example, in learning setting of an image, continuous image control is performed by curve interpolation between key frames using key frame data. As means to set image effects, developed is an apparatus capable of controlling an image with image control data which is obtained by curve interpolation of key frame data comprising time, position, size, zoom ratio and the like, using, for example, Bezier curve, for reproduction and display of the image.
Hereinafter, an example of a prior art image editing apparatus will be described with reference to FIG. 8. FIG. 8 is a block diagram illustrating an image editing apparatus disclosed in Japanese Published Patent Application No. Hei. 4-251027.
In FIG. 8, reference numeral 401 designates a key frame information input means for inputting key frame information comprising time on an image sequence, and other information. A key frame information storage unit 403 stores key frame information 402 output from the key frame information input means 401. An interpolation control point calculating unit 405 receives key frame information 404 output from the key frame information storage unit 403 and calculates interpolation control points 406. A timing generation means 408 generates timing control data 409 and 410 for reproducing an image at constant time intervals. A curve interpolation unit 407 receives the interpolation control points 406 output from the interpolation control point calculating unit 405 and the timing control data 409 output from the timing generation means 408, and periodically outputs image control data 412, such as coordinate data, to an image reproduction means 414. A storage unit 411 receives the timing control data 410 and periodically outputs image data 413 to the image reproduction means 414. The image reproduction means 414 controls reproduction of the image data using the image control data 412, and outputs the image data to a display unit 416.
A description is given of the operation of the image editing apparatus so constructed.
Initially, the key frame information input means 401 stores the key frame information 402 in the key frame information storage unit 403. The key frame information 404 is taken out of the key frame information storage unit 403 and input to the interpolation control point calculating unit 405 wherein control points for curve interpolation are calculated. Then, the curve interpolation unit 407 performs curve interpolation between key frames using the interpolation control points, providing image control data 412.
Next, the image reproduction means 414 displays an image on the display unit 416, using the image control data 412 and the image data 413 that is output from the storage unit 411 at a constant rate (for example, 30 frames/sec).
Using the image editing apparatus mentioned above, when a Bezier curve is generated, a Bezier curve passing an input point coordinate is obtained, whereby the shape and position of a curve to be drawn are grasped before they are input. As a result, drawing with a Bezier curve is realized using a favorable user interface.
In the prior art image editing apparatus, however, since all the key frames are subjected to identical curve interpolation, precise interpolation is not performed as shown in FIG. 9(a). That is, when four key frames, K0, K1, K2, K3, are input, the image protrudes from the display at the image display position P(tn) at time tn as shown in FIG. 9(b), i.e., so-called `overshoot` occurs. Further, in a key frame at which the motion of image suddenly changes (end point or mountain/valley point), key points must be added manually because the displayed image does not fit visual characteristics of human beings. Therefore, it is difficult to obtain a high grade image control effect easily.